Tinnitus is the perception of noise in the ears or head when no external sound is present. It is sometimes referred to as ringing in the ears, but people report hearing all kinds of sounds such as cricket chirps, whooshing, hissing, pulsing, and buzzing. It can vary in pitch from a low roar to a high squeal or whine, and may be heard in one or both ears. When the ringing is fairly constant, it can be annoying and distracting. As many as 50 million Americans suffer from tinnitus in some form. More than seven million people suffer severe and disabling symptoms significantly impacting their quality of life. Because tinnitus is associated with aging, and human longevity is increasing, the impact of tinnitus on society will likely get worse.
Despite the prevalence of tinnitus and its debilitating symptoms in many patients, the cause(s) of tinnitus imperative to precise prevention and treatment remain largely unknown. Currently, causes(s) and treatment(s) of tinnitus are especially difficult to identify because conventional testing techniques are unable to accurately and reliably detect and quantify tinnitus. One common detection and characterization method involves exposing a subject to several different sound patterns and asking the subject which sound pattern is the most qualitatively similar to the sounds he or she perceives. While this method is beneficial for detecting tinnitus is some subjects, it is not effective where the subject is unable to communicate with the test administrator or where the subject cannot perceive all of the effects of the subject's own tinnitus condition. Because this approach relies solely on the subject to explain his or her symptoms, this approach is also subject to malingering; a condition where a subject claims to have a medical problem, such as tinnitus, when such problem does not actually exist. There are many reasons for malingering related to tinnitus, one of which includes fraudulently collecting disability reimbursement. Currently, such fraud is a particular issue concerning military disability reimbursement. Another reason for malingering relates to psychiatric disorders suffered by subjects. A subject may believe he or she experiences tinnitus because he or she perceives sounds as a result of a psychiatric disorder when, in fact, no tinnitus actually exists.
In other cases, the subjects are animals and cannot reliably communicate with the test administrator. Animal models have been developed and used in an effort to improve detection techniques and prevention and treatment measures for tinnitus. Tinnitus may be modeled in animals by inducing a peripheral hearing loss, such as a loud sound exposure, which is a known cause of tinnitus in humans and performing behavioral tests to provide indicators of an animal's tinnitus. These behavioral tests require training animals to respond distinctively to the presence or absence of an acoustic stimulus. In some of these models, tinnitus is indicated when no external sound is present and the animals respond distinctively indicating that the animals hear sound. Because the behavioral training is based on the animals' ability to learn, remember, and voluntarily communicate with the test administrator, such animal models have inherent accuracy and implementation issues. In addition, the animal models typically require complex behavior manipulations (e.g., food or water deprivation, finely tuned shock parameters, variable reinforcement schedules) and weeks to months of complicated behavioral training. Thus, due to the subjective nature of tinnitus in both humans and laboratory animals, tinnitus testing techniques relying on the subjective response of the subject are generally problematic.
Similarly, current detection techniques relating to an objective response of the subject are insufficient to accurately and reliably detect and measure tinnitus. One objective detection method discussed in PCT application WO/02/47547 determines the presence of tinnitus by detecting the presence of pain. The method measures the electrical output of nerve fibers, which is associated with pain. However, such a method may not be appropriate for subjects experiencing pain from sources other than tinnitus. Moreover, this method describes determining the presence of tinnitus in a subject; it does not describe a method of objectively quantifying or determining the severity of the subject's tinnitus. The ability to quantify a subject's tinnitus is crucial to finding a proper and suitable treatment for a subject's tinnitus.
Objective methods of detecting other disorders having subjective symptoms, such as schizophrenia, include pre-pulse inhibition deficit testing. Schizophrenia has been associated with abnormalities in information processing, sometimes referred to as sensory gating failures. Gating generally allows for the screening or filtering of unimportant stimuli in order to respond and process important stimuli and related information. Sensory gating failures of subjects have been evaluated by analyzing the subject's pre-pulse inhibition deficit. All mammals respond to sudden intense stimuli (reflex stimulus) in modalities that consist of a series of flexion and extension responses (startle response). In humans, startle reflex magnitude diminishes when a weak pre-pulse stimulus precedes the reflex stimulus. Although identifying pre-pulse inhibition deficits has been advantageous in the detection of sensory gating failures related to schizophrenia, comparable tests for detecting the perception of sounds related to tinnitus have not been developed.
Thus, a need exists, in the testing of both human and animal subjects, for a method and apparatus to objectively measure tinnitus.